In the early 1980's several groups isolated and characterized growth hormone releasing factor (GRF).
GRF (also called Somatorelin) is a peptide secreted by the hypothalamus, which acts on its receptor and can promote the release of growth hormone (GH) from the anterior pituitary. It exists as 44-, 40-, or 37-amino acid peptide; the 44-amino acid form may be converted physiologically into shorter forms. All three forms are reported to be active, the activity residing mainly in the first 29 amino acid residues. A synthetic peptide corresponding to the 1-29 amino acid sequence of human GRF [hGRF(1-29)], also called Sermorelin, has been prepared by recombinant DNA technology as described in European Patent EP 105 759.
Sermorelin has been used in the form of acetate for the diagnosis and treatment of growth hormone deficiency.
GRF has indeed a therapeutic value for the treatment of certain growth hormone related disorders. The use of GRF to stimulate the release of GH is a physiological method in promoting long bone growth or protein anabolism.
It is well known that the natural form of GRF can suffer from chemical degradation in aqueous solution, primarily of Asn at position 8, which results in reduced biological potency (Friedman, A. R. et al., Int. J. Peptide. Protein Res., 37, 14-20, 1991; Bongers, J., et al., Int. J Peptide. Protein Res. 39, 364-374, 1992).
The main hydrolytic reactions occurring in GRF are sensitive to pH and reported to be: rearrangement of Asp3, at pH 4-6.5, cleavage of the Asp3-Ala4 bond at pH 2.5-4.5, deamidation and rearrangement of Asn8 at pH above 7 (Felix A. M. et al., Peptides, editors: Giralt E. and Andreu D., pp 732-733, Escom Publishers 1991). Due to the combined degradation pathways, unstabilized aqueous solutions GRF are most stable in the pH range 4-5. Bongers et al. (Bongers et al., 1992) have shown that the deamidation reaction at Asn8 increases rapidly as the pH is raised above pH 3.
WO 98/53844 describes stable liquid pharmaceutical compositions of hGRF containing nicotinamide and propylene glycol.
Various workers have made analogues of GRF by substitution of amino acids into the natural GRF sequence to improve the chemical stability (Serono Symposia USA, 1996; Friedman, 1991). While modification can be an effective means to improve the stability and retain bioactivity, it may be undesirable due to altered immunogenicity, which could be a problem for chronic therapies such as growth hormone deficiency.
According to EP 189 673 and U.S. Pat. No. 4,963,529 (Sumitomo Pharma Inc.) GRF formulations can be prepared by lyophilization and stabilized by human serum albumin or glycine. JP 3083931 and EP 417 930 describe a GRF-containing nasal preparation which is rendered low-irritating to nasal mucosa by adding sodium chloride and/or sugar alcohols, such as mannitol or sorbitol thereto.
In order that materials like hGRF be provided to health care personnel and patients, these materials must be prepared as pharmaceutical compositions. Such compositions must maintain activity for appropriate periods of time, must be acceptable in their own right to easy and rapid administration to humans, and must be readily manufacturable. In many cases pharmaceutical formulations are provided in frozen or in lyophilized form. In this case, the composition must be thawed or reconstituted prior to use. The frozen or lyophilized form is often used to maintain biochemical integrity and the bioactivity of the medicinal agent contained in the compositions under a wide variety of storage conditions, as it is recognized by those skilled in the art that lyophilized preparations often maintain activity better than their liquid counterparts. Such lyophilized preparations are reconstituted prior to use by the addition of suitable pharmaceutically acceptable diluent(s), such as sterile water for injection or sterile physiological saline solution, and the like.
Human GRF is found on the market in lyophilized formulations stabilized with mannitol GEREF®, Serono.